Cooling bearings, motors and other rotating heat generating components

ABSTRACT

Cooling apparatus for transferring heat from and cooling one or more heat generating components that support or drive a flywheel or other spinning member. The apparatus may include a first heat transfer element attached to and spinning with the spinning member, a second heat transfer element stationary with respect to the spinning member, wherein the first and second heat transfer elements move relative to one another, and wherein the first and second heat transfer elements are shaped and positioned in close proximity to one another so that substantial heat is transferred from the first heat transfer element to the second heat transfer element. Alternatively, the apparatus may include a set of rotating vanes mounted to rotate with the spinning member, an orifice configured to direct a spray of cooling liquid onto the rotating vanes, wherein the cooling liquid is sprayed onto the rotating vanes at a radially inward location, so that the liquid flows radially outward over the surface of the vanes as a thin film of liquid, and is thrown off the vanes by centrifugal action, and collecting apparatus configured to collect the liquid thrown off of the vanes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. application Ser. No. 11/330,896, filed on Jan. 12, 2006, nowallowed, all of which is hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to methods and apparatus for cooling bearings,motors, and other heat generating components that support and driverotating machinery, e.g., flywheels that are enclosed in a partialvacuum.

BACKGROUND

A control moment gyro (“CMG”) used for roll attenuation in boats isdependent on a heavy flywheel operating at high rotational speeds. Thespinning flywheel is supported by bearings that are subjected to highaxial and radial loads. As a result, these bearings produce asubstantial amount of friction-generated heat, which must be dissipatedin order to avoid dangerous heat build up. If the flywheel is supportedin a conventional, ambient environment, the heat can be dissipated byair convection, which can be assisted by having a fan blow air acrossthe outer and inner bearing races and the adjacent metal members. But ifthe flywheel is enclosed in a partial vacuum, e.g., as described in ourpatent, U.S. Pat. No. 6,973,847, there may not be enough air to permitconvection. The same cooling problem may exist in other devices in whichflywheels spin in partially evacuated enclosures (e.g., mechanicalenergy storage devices) and manufacturing processes that use evacuatedchambers containing spinning elements that require heat generatingbearings. At present, flywheel energy storage devices typically useexpensive magnetic bearings (which do not generate frictional heat)instead of much less expensive rolling element bearings. One reason isthat there are no proven methods of removing the heat from the innerraces of rolling element bearings in a partial vacuum except by jettingor circulating cooling oil through the bearings, and this tends tocreate large power losses.

Two types of heat flow—conduction and convection—need to bedistinguished. Heat conduction occurs by molecules bumping into othermolecules. Thus, when you place your hand on a warm radiator, the fastmoving molecules in the warm metal bump into molecules in your skin,transferring energy to them. Heat convection occurs when molecules aremoved as a consequence of air (or other gas or liquid) flowing from onelocation to another. Thus, the warm radiator heats a room by conductionof heat to air immediately adjacent the surface of the radiator, andthen by convection as that warmed air flows around the room. The warmthin the air is transferred to the occupants of the room by conduction,when the molecules in warm air contact the skin or clothing of theperson. Heat conduction may occur through a gas, liquid, or solid. Whenit occurs through a gas, it can be called gaseous conduction. When itoccurs through a solid (e.g., through a metal or other good conductor ofheat), it can be called solid conduction.

Fourier's law of heat conduction defines one dimensional heat transferbetween two parallel surfaces by gaseous conduction:Q=KAΔT/ΔXWhere

Q=heat transfer (watts)

K=thermal conductivity of the gas (watts/m-Deg C)

A=area of the parallel surface (m2)

ΔT=temperature differential between the two heat transfer surfaces (degC)

ΔX=distance between the heat transfer surfaces (m)

As shown in the equation, the amount of heat transferred is directlyproportional to the thermal conductivity of the gas, the area of thesurfaces, and the temperature difference between the surfaces, and isinversely proportional to the distance between the surfaces. The thermalconductivity of the gas (K) is constant irrespective of pressure untilthe pressure is so low that the gas molecular mean free path is equal toor greater than the distance between the surfaces (ΔX). This means thatthe amount of heat transferred will be independent of pressure until thegas mean free path is equal to or greater than the distance between thesurfaces. Below the pressure where the gas molecular mean free path isgreater than the distance between the surfaces, the gas molecules willcontinue to conduct heat but now there is a reduction in the thermalconductivity (and the amount heat transferred) with further reductionsin the gas pressure.

SUMMARY

We have discovered practical techniques for transferring heat away fromheat generating components, e.g., bearings and motors, that support anddrive rotating machinery such as flywheels. Typically, heat will buildup on the inner races of the bearings that support the flywheel (butother sources of heat, such as motor heat, air drag or windage are alsopossible). Such a build up of heat on the inner races can lead tofailure of the apparatus, as a large temperature differential can resultbetween the inner and outer bearing races. The outer races typicallyremain cooler because heat can flow (by conduction through abuttingmetal members) from the outer races to the exterior of the enclosure,where the heat is dissipated by convection (air passing across the warmexterior surface). Only a small amount of heat is conducted across thebearings (from the inner to outer races), and thus the inner races andthe flywheel to which they are attached tend to rise in temperature. Therising temperatures can destroy the effectiveness of bearing lubricant,and can also subject the inner race to thermal expansions not seen bythe cooler outer race with resulting catastrophic destruction of thebearings and apparatus.

Known cooling techniques include immersing the bearings in a circulatingoil bath or jetting oil through the bearings (as in a gas turbineengine) or pumping a large volume of air/oil mist through the bearings(as in machine tool spindles) to lubricate and cool them. However, thesemethods are complicated and they tend to increase the heat generated bythe bearing as the viscous drag of the rolling elements churning throughthe oil substantially increases the power required to drive the flywheelor other spinning member. The air/oil mist method is not applicable tovacuum applications as it requires substantial air flow. Some machinetool manufacturers pump water down a hole that is gun drilled throughthe spindle shaft to remove heat from the bearings and motor. This isalso difficult to apply to vacuum applications as the water must bemaintained at ambient pressure to prevent it from vaporizing.

In a first aspect, the invention features cooling apparatus fortransferring heat from and cooling one or more heat generatingcomponents that support or drive a flywheel or other spinning member.The apparatus comprises a first heat transfer element attached to andspinning with the spinning member, a second heat transfer elementstationary with respect to the spinning member, wherein the first andsecond heat transfer elements move relative to one another, and whereinthe first and second heat transfer elements are shaped and positioned inclose proximity to one another so that substantial heat is transferredfrom the first heat transfer element to the second heat transferelement. The close proximity of the two surfaces or elements promotesheat transfer by gaseous conduction. The relative rotational movementand close proximity of the elements creates rotating cavity flows thatpromote heat transfer by gaseous convection. These rotating flowscontinually circulate air molecules from the hotter first element to thecooler second element.

In preferred implementations, one or more of the following may beincorporated. Heat transfer between the first and second heat transferelements may occur both by gaseous conduction and convection. Heattransfer between the first and second heat transfer element may beprimarily by gaseous conduction. The first and second heat transferelements may have closely spaced exposed surfaces across which heat istransferred. The first heat transfer element may comprise a plurality offirst vanes, the second heat transfer element may comprise a pluralityof second vanes, the first vanes may move with respect to the secondvanes, the first vanes may extend into gaps between the second vanes sothat the first and second vanes are interleaved, and substantial heatmay be transferred from the first vanes to the second vanes. Anenclosure may surround the spinning member, the first heat transferelement may comprise the outer surface of the spinning member, and thesecond heat transfer element may comprise the inner surface of theenclosure spaced by a small gap from the spinning member so thatsubstantial heat is transferred by gaseous conduction from the spinningmember to the enclosure. The separation between the first vanes andsecond vanes may be greater than 0.025 mm but less than 10 mm. Thespinning member may be enclosed within an enclosure containing a gas atbelow-ambient pressure or below-ambient density, the first heat transferelement and first vanes may spin relative to the enclosure, the secondheat transfer element and second vanes may be fixed relative to theenclosure, and the second heat transfer element may be positioned sothat heat can be readily transferred from the second heat transferelement to the exterior of the enclosure. The gas may be bothbelow-ambient pressure and below-ambient density. The axis of rotationabout which the spinning member spins may define an axial direction, thefirst vanes may be cylindrical elements extending in a first axialdirection from a first base attached to the spinning member, the secondvanes may be cylindrical elements extending in a second axial direction,opposite the first axial direction, from a second base attached to theenclosure, and the gaps between the second vanes may be cylindricalchannels shaped and positioned to receive the cylindrical first vanes.The axis of rotation about which the spinning member spins may define anaxial direction, the first and second vanes may be planar elementsextending in radial directions perpendicularly to the axial direction,and the gaps between the second vanes may be planar channels shaped andpositioned to receive the planar first vanes. The first and second heattransfer elements may be located adjacent a bearing that supports thespinning member, the bearing may have an inner race and an outer race,the first vanes and inner race may be attached to the spinning member soheat flows by conduction from the inner race to the first vanes and fromthe spinning member to the first vanes, the outer race may be attachedto the enclosure, and the inner race, spinning member, first vanes andsecond vanes may be sized and positioned so that heat from the innerrace of the bearing flows by solid conduction from the inner race to thespinning member and to the first vanes, by solid conduction from thespinning member to the first vanes, and by gaseous conduction andconvection from the first vanes to the second vanes, and by solidconduction from the second vanes to the exterior of the enclosure. Theapparatus may comprise at least two bearings, each with its own firstand second heat transfer elements as described. The spinning member maybe a flywheel and the flywheel and enclosure may be part of gyroscopicroll stabilizer for a boat. The invention may further comprise a heatsink to which heat flows from the second vanes. The heat sink maycomprise air-cooled fins on the exterior of the enclosure. The gasbetween the first and second transfer elements may have a molecular meanfree path equal to or less than the distance between the heat transferelements. The invention may further comprise a plurality of sets offirst and second vanes. The gas may have a higher thermal conductivitythan air. The heat generating component may comprise one or morebearings. The heat generating component may comprise one or moreelectrical motors.

The gap between the hotter rotating vanes and the cooler non-rotatingvanes may be kept very small, and thus provide a heat path to theexterior of the device as long as the rotating vanes are hotter than thestationary vanes. Heat may be conducted from the heat generatingcomponents to the rotating vanes by solid conduction, then across theair gap to the stationary vanes by gaseous conduction and convection andthen by conduction and convection to the atmosphere or a heat sink.

This first aspect of the invention has significant advantages. Forexample, as applied to ambient and above ambient pressure conditions, itdoes not require pumping large volumes of air or cooling fluid to coolthe heat generating components. However, even greater advantages arefound at below ambient pressure, wherein convective cooling with airbecomes more difficult because of the reduced pressure, and radiant heattransfer may be negligible because the temperature differentials may notbe large enough to transfer a significant amount of heat. Reliance ongaseous conduction benefits from the fact that the thermal conductivityof a gas increases with temperature so that as the gas warms up it willconduct more heat across the gap (for a fixed temperature differential)between the rotating and stationary vanes. This helps stabilize thermalbehavior.

Rotating cavity flows will exist in the small gaps between the fixed androtating vanes even in a partial vacuum. In some applications, the gasdensity and/or rotational speed will be high enough that gaseousconvection will augment the gaseous conduction cooling. The rotatingflow circulates the gas molecules so they are continuously transportedfrom the hot rotating vanes to the cooler stationary vanes.

The first aspect permits heat to be removed passively withoutcirculating any fluids inside the enclosure. This considerablysimplifies the device or machine, as a coolant pump, motor, filter andheat exchanger are not required. Grease lubricated bearings can be usedand these will have less frictional torque than oil lubricated bearings.

In a second aspect, the invention features cooling apparatus fortransferring heat from and cooling one or more heat generatingcomponents that support or drive a flywheel or other spinning member.The apparatus comprises a set of rotating vanes mounted to rotate withthe spinning member, an orifice configured to direct a spray of coolingliquid onto the rotating vanes, wherein the cooling liquid is sprayedonto the rotating vanes at a radially inward location, so that theliquid flows radially outward over the surface of the vanes as a thinfilm of liquid, and is thrown off the vanes by centrifugal action; andcollecting apparatus configured to collect the liquid thrown off of thevanes.

Preferred implementations of this aspect of the invention mayincorporate one or more of the following. The invention may furthercomprise cooling apparatus configured to cool the liquid collected bythe collecting apparatus, and wherein the cooled liquid may be returnedto the orifice. There may be a plurality of sprays of cooling liquid,each stream may be narrower than the gap between the rotating vanes, andeach stream may be directed so that it generally travels between thevanes to the radially inward location. The cooling liquid may be an oil.The spinning member may be enclosed within an enclosure containing a gasat below-ambient pressure or below-ambient density, the rotating vanesmay rotate with the spinning member within the enclosure, and theorifice may be fixed relative to the enclosure. The vapor pressure ofthe cooling liquid may be lower than the operating pressure of the gaswithin the enclosure. There may be a plurality of sets of rotatingvanes. The oil used for cooling may also be used for lubrication of atleast one bearing.

The liquid cooling aspect of the invention has significant advantages.For example, the cooler liquid film moving at high speed across thehotter surface of the rotating vanes makes for a very efficient heatexchanger. The oil exiting the vanes can be readily collected andcooled, either passively or actively, and then returned to the orificeto be sprayed on the vanes again.

For very high-speed flywheel bearings, oil lubrication is mandatory andin this case the liquid cooling scheme has an advantage, as oil can beused for cooling and lubricating the bearings. The amount of oilrequired to lubricate the bearings is very small. Therefore, jetting theoil onto the rotating vanes for cooling requires far less power thanjetting or circulating the oil through the bearings as in traditionalbearing cooling schemes.

Both the first and second aspects of the invention overcome the problemof cooling rotating components that generate heat and are enclosed in apartial vacuum. They both will permit the development of control momentgyros (CMGs) for stabilizing small boats and the development of flywheelenergy storage devices that use rolling element bearings, as now thereis a way of removing the heat from these rotating components that doesnot increase operating power requirements. Additionally, the inventionmay assist in cooling the inner races of bearings, motors and otherrotating heat generating components that operate in confined spaces atambient or above ambient pressure (e.g. machine tool spindles).

Other features and advantages of the invention will be found in thedetailed description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a boat stability CMG incorporatingan implementation of the first aspect of the invention.

FIG. 2 is an enlargement of the upper bearing portion 2-2 of FIG. 1.

FIG. 3 is an enlargement of the lower bearing portion 3-3 of FIG. 1

FIG. 4 is a cross-sectional view (taken along 4-4 in FIG. 5) through theouter heat transfer element of the implementation of FIG. 1.

FIG. 5 is a plan view (taken along 5-5 in FIG. 4) looking up at thevanes of the heat transfer element of FIG. 4.

FIG. 6 is an elevation view of the heat transfer element of FIG. 4.

FIG. 7 is a plan view (taken along 7-7 in FIG. 6) looking down at thetop surface of the heat transfer element of FIG. 4.

FIG. 8 is a cross-sectional view (taken along 8-8 in FIG. 9) through theinner heat transfer element of the implementation of FIG. 1

FIG. 9 is a plan view (taken along 9-9 in FIG. 8) looking down at thetop surface of the inner heat transfer element of FIG. 8.

FIG. 10 is a cross-sectional view of a boat stability CMG incorporatinga liquid cooling implementation of the second aspect of the invention.

FIG. 11 is an enlargement of the upper bearing portion 11-11 of FIG. 10.

FIG. 12 is an enlargement of the upper bearing portion 12-12 of FIG. 10

FIG. 13 is an elevation of the set of rotating vanes of theimplementation of FIG. 10.

FIG. 14 is a cross-sectional view of the set of rotating vanes of FIG.13.

DETAILED DESCRIPTION

There are a great many possible implementations of the invention, toomany to describe herein. Some possible implementations that arepresently preferred are described below. It cannot be emphasized toostrongly, however, that these are descriptions of implementations of theinvention, and not descriptions of the invention, which is not limitedto the detailed implementations described in this section but isdescribed in broader terms in the claims.

Shown in FIG. 1 is a gyroscopic roll stabilizer 10 for small boats (ofthe type described in U.S. Pat. No. 6,973,847, incorporated herein byreference). A steel flywheel 12 spins within an aluminum enclosure 14,which is evacuated to a below-ambient pressure, and may include abelow-ambient density gas (e.g., helium or hydrogen) to reduce frictionon the spinning flywheel. An electric motor (frameless DC brushless) 16integrated within the interior of the enclosure drives the flywheel,which is supported by an upper bearing assembly 18 and lower bearingassembly 20.

As shown in the enlargements of FIGS. 2-3, each bearing assemblyincludes an outer housing 22, 24, outer race 26, 28, inner race 30, 32,and balls 34. Seals 36 are provided on both the top and bottom of eachbearing. Upper and lower retainers 40, 42 hold the upper bearing inplace. These bearings are lubricated by a grease pack.

Heat generated by the bearing inner races and electric motor rotor, istransferred to the exterior by cooling collar assemblies 50, 52 (one ofmany implementations of the heat transfer elements) located adjacenteach bearing. Each cooling collar assembly includes an inner rotatingcollar 54, 56, and an outer stationary collar 58, 60 that also forms theenclosure end cap. Collars 54, 56, 58, 60 may be constructed of avariety of materials with good heat conductivity (e.g., aluminum,copper, or plastic).

As shown in FIGS. 4-5, the outer collars 58, 60 have ten cylindricalvanes 62, each of a different radius. Cylindrical gaps 64 are formedbetween the vanes. The vanes are approximately 2.77 mm in radialthickness, and the radial separation between vanes (i.e., the radialwidth of the gaps) is approximately 4.78 mm. The vanes 62 are about 32mm in length along the axial direction.

The inner collars 54, 56 have eleven cylindrical vanes 66 andcylindrical gaps 68 between the vanes (FIGS. 2-3), each of a differentradius, and sized and positioned so that the vanes 66 mate with vanes 62of the mating outer collars. Vanes 66 are approximately the same length(32 mm), width, and radial thickness as vanes 62, and are received ingaps 64 between vanes 62.

After inner and outer collars are mated, with vanes interleaved, theradial separation between a rotating vane from one collar and astationary vane from another is approximately 1 mm. To improve heattransfer by gaseous conduction, this separation may be made as small aspossible subject to practical limitations such as machining andoperating tolerances. In partial vacuum applications, the separation istypically not less than the mean free path of the gas molecules at theoperating pressure. This small separation ensures that the gas thermalconductivity is not reduced by the vacuum pressure and assists heattransfer by gaseous convection.

In one implementation, the operating pressure is 1 Torr, the operatingtemperature is 100 C, and the molecular mean free path of air is 0.066mm, which is significantly less that the 1 mm radial separation Inpractice, the distance may vary from these general guidelines so long assubstantial heat is transferred across the separation.

As shown in FIGS. 6-7, the exterior surfaces of outer collars 58, 60have additional heat transfer vanes 70, which transfer heat from thecollar to the surrounding atmosphere (by conduction at the surface ofthe vanes, with convection moving air past the vanes).

In the implementation shown, the rotating and stationary vanes 66, 62each have a total surface area of 0.34 square meters. A typicaltemperature differential between the rotating and stationary vanes is 15C, and air conduction alone will transfer 153 watts across the gap tocool the bearing inner race at this differential. If it is necessary toprovide more cooling, the stationary vanes could be actively cooled byblowing air over them (outside the containment) to create a biggertemperature differential between the rotating and stationary vanes. A 30C temperature differential would transfer 306 watts by gaseousconduction alone. Alternatively, the amount of heat transfer could beincreased by back filling the vacuum chamber with helium or hydrogenafter the initial pump down. Helium's thermal conductivity isapproximately 5.6 times that of air, and therefore a 15 C temperaturedifferential would transfer 855 watts of heat by gaseous conductionalone. If further increases in heat transfer were required the radialseparation between the fixed and rotating vanes could be reduced from 1mm to 0.5 mm. It is typically feasible to operate with that small aradial separation as machines like CMGs and flywheel energy storagedevices are typically manufactured to very tight tolerances (less than0.025 mm typically), and their flywheels are supported in very highprecision rolling element bearings. If the flywheel is enclosed inhelium at 1 Torr, the radial separation is 0.5 mm, and the temperaturedifferential is 15 C, then 1710 watts of heat can be transferred fromthe bearing inner races by gaseous conduction alone. It is also possibleto adjust the amount of heat transferred by increasing or decreasing thesurface area of the vanes.

These examples show how the cooling method and apparatus can be adjustedto provide the amount of cooling that the heat generating componentsrequire in order to achieve stable operating temperatures. The designercan vary the vane area, radial separation, gas type, gas density and thetemperature difference between the rotating and stationary vanes to getthe optimum solution for a specific application.

FIGS. 10-14 show an implementation of the liquid cooling scheme. Theliquid cooling implementation also depends on cooling collars on therotating shaft adjacent to the primary source of heat, i.e., the innerrace of the flywheel bearings. However, with liquid cooling, the fins onthe collars consist of spaced planar disks extending radially outwardfrom the shaft, and there are no mating fixed fins attached to theflywheel containment. Rather, cooling is accomplished by oil jetspositioned on the containment outboard of the disks which squirt streamsof oil between the rotating disks and toward the center of the flywheelshaft, thus conducting the heat from the disks to the oil, which is thenflung by centrifugal force outward to be collected by an inner linerinside the containment but outside the perimeter of the flywheel. This,in turn, forces the hot oil to follow the inner curvature of thecontainment on its downward gravitational path, where it transfers theheat to the containment, aided by interior ridges on the containmentwhich increase the surface area contacted by the oil. The oil iscollected in a sump at the bottom of the device, where it is pumped backup to the oil jets, completing the cooling cycle.

Turning to FIG. 10, the heat generated by the bearing inner races andelectric motor rotor, is transferred to upper and lower cooling collarassemblies 71, 72 located adjacent to the upper and lower bearing innerraces 73, 74. In the case of the upper bearing, a stationary housing 75surrounds the upper cooling collar and forms the enclosure end cap. Inthe case of the lower bearing, the stationary housing 76 surrounding thelower cooling collar is part of the oil reservoir assembly 77.

The reservoir assembly also contains the cooling oil 78, cooling pump79, cooling pump motor 80, and a filter and valves (not shown). Thecooling collar assemblies 71, 72 may be constructed of a variety ofmaterials that have good thermal conductivity (e.g. aluminum andcopper).

As shown in more detail in FIGS. 11-14, the cooling collar assemblieseach have 4 horizontal vanes that form 3 gaps between the vanes. Theinner radius of the gaps is 54 mm, the outer radius is 89 mm, and thewidth of the gaps is 2.4 mm. The upper and lower stationary housingsthat surround the cooling collars each contain 3 oil jets 81 (one pergap). These jets are mounted and oriented such that they spray a streamof cooling oil into and parallel to the gaps between the horizontalvanes. The jet orifice diameter is 0.64 mm where the stream exits.

The very thin stream of cooling oil contacts the bottom of each gap inthe cooling collar vanes and is redirected by the high speed of rotationsuch that it creates a thin film that completely covers the vanesurfaces before centrifugal forces throw the film off. The cooler oilfilm moving at high speed across the hotter vane surface picks up heatby conduction and carries it away by convection. The result is veryefficient heat transfer from the inner race of the bearing to thecooling collar, and then to the cooling oil.

The heated oil exiting the upper collar vanes strikes the stationaryhousing 75, drops through holes in the bearing housing 82 and iscollected by an inner liner 83 inside the containment but outside theperimeter of the flywheel 84. The liner is mounted to interior ribs ofthe containment 85 to increase the surface area in contact with the oil.This liner/rib arrangement forces the hot oil to follow the innercurvature of the containment on its downward gravitational path to thereservoir below the lower bearing. As the oil follows this contour, ittransfers heat to the cooler containment, which steadily decreases theoil temperature until it reaches the reservoir 77.

There may also be a bypass oil flow that is sprayed on the containmentbetween the ribs and liner just below the upper bearing. This bypassflow increases the amount of oil in contact with the containment andhelps cool the oil in the reservoir.

The hot oil exiting the vanes of the lower collar 72 drops into thereservoir 77 without significant cooling. At any point in time, thereservoir contains a mix of oil from the upper collar that has beencooled by the containment, bypass oil that has been cooled by thecontainment, and oil from the lower collar that has not been cooled. Thecontainment's internal and external surface areas and external coolingmay be designed so that sufficient heat is extracted from the oilexiting the upper collar and from the bypass oil flow to cool the mix ofoil in the reservoir. The oil in the reservoir is picked up by the pumpand pumped back up to the oil jets and sprayed on the upper and lowercollars and through the bypass jets, thus completing the cooling cycle.

This particular cooling collar implementation has a total vane surfacearea of 0.093 square meters in contact with oil. The oil pump delivers0.5 liter per minute per collar or 0.165 liter per minute per jet. Thetemperature of the oil increases 15 deg C. (from its entry onto thevanes to its exit from the vanes) to transfer 250 watts of heat from thebearing inner race and maintain the inner race at a temperature in therange of 80-100 C.

Like the scheme of FIGS. 1-9, the liquid cooling scheme is flexible ifit is necessary to provide more cooling. The cooling vane area, numberof gaps/jets, and cooling flow rate can all be increased to increase therate of heat transfer from the bearing inner races and motor to thecontainment. If the oil used for heat transfer is not sufficientlycooled by the containment, then forced air cooling can be applied to theexterior of the containment. Alternatively, the reservoir oil can becirculated through a dedicated oil/air or oil/water heat exchanger toextract more heat from the oil and further lower the oil's temperatureprior to spraying it on the collars.

Additionally, in some very high-speed flywheel applications, it may benecessary to use oil instead of grease to lubricate the bearings. Inthese cases, the same oil used for heat transfer with the coolingcollars can be used for lubricating the bearings. The amount of oilrequired to lubricate the bearings is very small. Therefore it can bedelivered by a number of methods including jetting, micro dosing,wicking or by letting a small amount of the oil exiting the collar vanesenter the bearing.

Many other implementations other than those described above are withinthe invention, which is defined by the following claims. As mentionedearlier, it is not possible to describe here all possibleimplementations of the invention, but a few possibilities not mentionedabove include the following:

Implementations of the first aspect of the invention may includemultiple vane or collar assemblies installed on a single shaft to cool anumber of heat generating components or improve cooling of onecomponent. Gases which have higher thermal conductivities and specificheats than air (e.g. helium and hydrogen) may be used to improve theheat transfer in partial vacuum and enclosed applications. The vaneassemblies may be constructed of good heat conducting metals (such ascopper and aluminum) or thermally conductive plastics.

Gaseous conduction and convective cooling may be provided by keeping thegap between the flywheel and its enclosure very small, therebypermitting heat to flow from the flywheel rim and/or disc to the coolerenclosure. This arrangement may provide a second path of heat transferor it may be the principal heat transfer path.

Liquid cooling implementations may include multiple vane or collarassemblies installed on a single shaft to cool a number of heatgenerating components or improve cooling of one component. If oil isused as the coolant fluid, it can also be used to lubricate thebearings. The vane assemblies may be constructed of good heat conductingmetals (such as copper and aluminum) or thermally conductive plastics.The fluid used for cooling could be oil, water, or a heat transferfluid.

Both the first and second aspects of the invention will work in apressured environment, at ambient pressure, or in a partial vacuum.

As used in the claims, when an element is said to be “attached to”another element that includes the case of there being one or moreintermediate elements between the elements, as well as the case in whichthe elements are in direct contact.

Not all of the features described above and appearing in some of theclaims below are necessary to practicing the invention. Only thefeatures recited in a particular claim are required for practicing theinvention described in that claim. Features have been intentionally leftout of claims in order to describe the invention at a breadth consistentwith the inventors' contribution. For example, although in someimplementations, interleaved vanes are used to transfer heat, suchinterleaved vanes are not required to practice the invention of otherclaims. Although in some implementations, liquid coolant is circulatedover vanes, liquid coolant is not required to practice the invention ofother claims.

What is claimed is:
 1. A gyroscopic roll stabilizer for a boat, thestabilizer comprising: a flywheel, the flywheel being configured to bespun about a spin axis; a first plurality of vanes coupled to theflywheel such that the first plurality of vanes spin with the flywheelrelative to an enclosure; a second plurality of vanes fixed relative tothe enclosure and the flywheel such that the first plurality of vanesspin with respect to the second plurality of vanes, the second pluralityof vanes defining gaps into which the first plurality of vanes extend sothat the first and second plurality of vanes are interleaved; at leastone rotating heat generating component coupled to the flywheel andpositioned such that heat is transferred from the heat generatingcomponent to the first plurality of vanes; the enclosure surrounding thefirst plurality of vanes, the second plurality of vanes, the heatgenerating component, and a portion or all of the flywheel, theenclosure containing a below-ambient density gas and maintaining abelow-ambient pressure, wherein the below ambient density gas has athermal conductivity at least 5 times greater than air; and wherein theflywheel, the first plurality of vanes, the second plurality of vanes,the heat generating component, the enclosure, and the gimbal structureare configured so that, when installed in the boat, the stabilizer dampsroll motion of the boat.
 2. The stabilizer of claim 1 wherein: the heatgenerating component includes at least one bearing supporting theflywheel, the bearing having an inner race and an outer race; and thebearing is located adjacent the first plurality of vanes such that heatflows from the inner race to the first plurality of vanes, from thefirst plurality of vanes to the second plurality of vanes, and from thesecond plurality of vanes to the exterior of the enclosure.
 3. Thestabilizer of claim 2 wherein the first plurality of vanes and thesecond plurality of vanes are sized and spaced such that heat flows fromthe first plurality of vanes to the second plurality of vanes by gaseousconduction.
 4. The stabilizer of claim 3 wherein the below-ambientdensity gas is hydrogen.
 5. The stabilizer of claim 3 wherein thebelow-ambient density gas includes helium.
 6. The stabilizer of claim 5wherein: the first plurality of vanes are cylindrical elements extendingin a first direction substantially parallel to the spin axis; the secondplurality of vanes are cylindrical elements extending in a seconddirection substantially parallel to the spin axis and opposite the firstdirection.
 7. The stabilizer of claim 5 further comprising a heat sinkconfigured such that heat flows from the second plurality of vanes tothe heat sink.
 8. The stabilizer of claim 7 wherein the heat sinkcomprises air-cooled fins on the exterior of the enclosure.
 9. Thestabilizer of claim 5 wherein a distance between the first plurality ofvanes and the second plurality of vanes is less than 5 mm.
 10. Thestabilizer of claim 5 wherein the enclosure maintains a below-ambientpressure of less than 390 torr (0.5 atmosphere).
 11. The stabilizer ofclaim 1 wherein the first plurality of vanes and the second plurality ofvanes are sized and spaced such that heat flows from the first pluralityof vanes to the second plurality of vanes by gaseous conduction.
 12. Thestabilizer of claim 11 wherein a distance between the first plurality ofvanes and the second plurality of vanes is less than 5 mm.
 13. Thestabilizer of claim 1 further comprising: a flywheel drive motorconfigured to spin the flywheel about a spin axis; and a device forapplying a torque to the flywheel.
 14. A method of stabilizing a boat,the method comprising: spinning a flywheel about a spin axis; permittingflywheel precession; spinning a first plurality of vanes with theflywheel relative to an enclosure, wherein at least one rotating heatgenerating component is positioned such that heat is transferred fromthe heat generating component to the first plurality of vanes;maintaining a second plurality of vanes fixed relative to the enclosureand the flywheel such that the first plurality of vanes spin withrespect to the second plurality of vanes, the second plurality of vanesdefining gaps into which the first plurality of vanes extend so that thefirst and second plurality of vanes are interleaved; and wherein theenclosure surrounds the first plurality of vanes, the second pluralityof vanes, the heat generating component, and a portion or all of theflywheel, the enclosure containing a below-ambient density gas andmaintaining a below-ambient pressure, wherein the below ambient densitygas has a thermal conductivity at least 5 times greater than air. 15.The method of claim 14 wherein: the heat generating component includesat least one bearing supporting the flywheel, the bearing having aninner race and an outer race; and the bearing is located adjacent thefirst plurality of vanes such that heat flows from the inner race to thefirst plurality of vanes, from the first plurality of vanes to thesecond plurality of vanes, and from the second plurality of vanes to theexterior of the enclosure.
 16. The method of claim 15 wherein the firstplurality of vanes and the second plurality of vanes are sized andspaced such that heat flows from the first plurality of vanes to thesecond plurality of vanes by gaseous conduction.
 17. The method of claim16 wherein the below-ambient density gas includes helium.